With the increasing application in the power system, the High Voltage Direct Current (HVDC) technology has been a key technology in the safety power system. The HVDC thyristor valve has play a best important role and its stability has been the key factor to ensure the power system safe. The operation test of the thyristor is a primary means to test the HVDC thyristor design and manufacture technology level, improve its stability. The fault current test is one important part of the operation test of the thyristor. The aim of the fault current test is testing whether the maximum current, voltage and temperature effect design proper or not when the short-circuit passes through the thyristor. The test includes two following test mainly:
a) Single wave fault current test with the forward voltage—inhibit one of the largest amplitude single wave fault current, begin with the maximum temperature followed by the closing the reverse voltage and forward voltage including all load over-voltage.
b) Multi-wave fault current test without the forward voltage—under the same condition to the single wave fault current test, the multi-wave fault current will not stop until the circuit breaker trips, but there is no forward voltage in the period and voltage will not be added after last fault current wave pass through.
At present, synthesis methods are generally adopted internationally to carry out the direct current thyristor fault current test. For example, the patent which number is 200810236505.2 provided “a synthesis method of high voltage direct current thyristor operation test”. After acquiring the energy from the power system, provide another current source to test the sample thyristor valve. This method adopted independent current source and voltage source. This reduced the test equipment volume and the operation cost. But this method is similar to that of ABB Company and Siemens Company. They all adopted high-current loop six pulse rectifier bridges to provide fault current by simulating the bridges short-circuit, to provide test voltage by resonant high voltage circuit. This method suffered from the following disadvantages: a greater impact on power system, requiring the power support system has a very high short-circuit capacity. This is harmful to the stability of voltage of the power support system, and also easily affects the normal operation of other loads. This greatly reduced the safety and reliability of the test equipment. What's worse, the peak current supplied by the power system and the current duration is adjustable poorly and inflexible.